The invention relates to a precision force transducer with a spring element whose load-dependent deflection is converted into an electrical signal using strain gauge elements.
Precision force transducers of this kind are generally known and are described, for example, in German Publication DE 195 11 353 C1.
If the accuracy of this precision force transducer is to be increased, creep and hysteresis in particular are significant problems. One approach to achieve an improvement was to use low creep steel grades subjected to special heat treatments—so-called maraging steels, for example. Nanostructured austenitic steels with block dislocation have also been proposed (German Laid Open Publication DE 198 13 459 A1). Another approach to solve this problem is to use aluminum alloys. Creep of this material is compensated by reverse creep of the conventional strain gauges. Creep of conventional strain gauges is due to the polymer film forming the base layer of the strain gauge and the adhesive used between the strain gauge and the spring element. However, because the temperature dependence of the two creep effects differs, this compensation is successful, at best, in a narrow temperature range. However, all of these known solutions allow a meaningful resolution of the precision force transducer of only approximately 50,000 increments. Thus, if the precision force transducer is used for calibratable scales, only approximately 3×3000 calibratable increments are possible.
Another error effect in conventional strain gauges is the moisture sensitivity of the adhesive layer and the substrate film. High-resolution precision force transducers can be encapsulated against the influence of moisture only to a limited extent because of force shunting. Therefore the moisture sensitivity of a conventional strain gauge is another factor limiting resolution in the construction of precision force transducers.